Military strike aircraft are designed to carry, release, and deliver a wide range of weapons and other "stores" (bombs, for example) while in flight. Aircraft used to deliver stores in flight typically incorporate suspension and release equipment (S&RE), such as ejector racks, that are located beneath the wings and fuselage and are designed to forcibly release the stores upon command. Typical ejector racks are disclosed in U.S. Pat. Nos. 4,043,525 and 4,347,777, both of which are assigned to an affiliate of the entity to which the present invention is assigned.
In a typical stores release and ejection system, a mechanism is activated that mechanically releases and forcibly ejects the store from the aircraft upon command. During the ejection process, ejection pistons or rams housed within the S&RE equipment are forced outward against the store and cause the store to be forcibly ejected away from the aircraft body. These rams are extended outward in a matter of milliseconds at extremely high loads, potentially producing considerable mechanical shock to both the ejection ram and the store. If proper precautions are not observed, these high loads may result in damage to the ejection rams or to the store itself. Limiting mechanical shock loads to the store has become increasingly important with the increasing use of smart weapons incorporating shock-sensitive electronic equipment.
A typical ejection ram comprises a single piston or a set of coaxial telescoping pistons and is packaged in a structural housing that provides some length for ram extension. The structural housing also provides surfaces for stopping the motion of the ram as well as surfaces for fluid sealing piston rings to travel along. During ejection, high pressure fluid (either gas or liquid) is introduced into the housing, forcing the piston outward and in turn ejecting the store.
Early ejector racks typically utilized pyrotechnic cartridges as an energy source for supplying high-pressure fluid to the ejection rams. While pyrotechnic charges provide a weight-efficient ejection power source, they generate significant residue, require frequent cleaning and other maintenance, pose a safety hazard, and exhibit other undesirable limitations.
Some newer ejector rack designs employ a combination of pressurized gas and hydraulics to operate pneumatic ejector mechanisms. In these systems, pressurized gas is stored in an accumulator and is used to transfer ejection energy to a fluid that in turn actuates ram ejectors upon command. Such an apparatus is disclosed in U.S. Pat. No. 4,095,762 to Holt. The Holt apparatus has several undesirable limitations, however, including excessive weight, a complex two-fluid (gas and liquid) system, complicated maintenance requirements, and an inability to compensate for changes in outside pressure and temperature during flight.
A further improvement in ejector rack design is disclosed in U.S. Pat. No. 5,583,312 to Jakubowski, in which a pneumatic ejector rack having a single on-board pressurization system for initiating multiple release mechanisms is disclosed. U.S. Pat. No. 5,583,312 is incorporated herein by reference. The Jakubowski system uses filtered pressurized air as both an energy source and an energy transfer medium and thus requires no hydraulics. Since the compressor system is on-board, a constant pressure may be maintained independent of outside temperature and pressure changes. In operation, the pressurized gas from the accumulator, when released through a feed port, opens store release hooks and simultaneously forces ejector pistons outward, thereby forcibly releasing and jettisoning the store.
To minimize mechanical shock during ejection, the aforementioned ejector racks typically employ screws or other mechanical means to adjust the ejection rams against the store body during weapons loading operations on the ground. One such means is a threaded contact foot which can be extended to be in contact with the store after the store has been loaded into the ejector rack. While the threaded contact foot works well to place the ejection ram into contact with the store and thus to minimize mechanical shock to the store upon ejection, use of the threaded contact foot imposes several limitations. First, so that the extended contact foot does not interfere with loading of a new store, each contact foot must be manually retracted prior to loading new stores onto the ejector rack. Second, each contact foot must be manually adjusted to contact the store during store loading, since stores of varying sizes must be accommodated. These manual operations increase cost and ground turnaround time.
A second means to eliminate gaps between the ram pistons and the store in conventional S&RE ejector racks, and thus to minimize mechanical shock to stores upon ejection, includes a pre-load spring within the piston to automatically bias the ejection ram into contact with the store after loading. If sufficient spring play is provided, a range of store sizes can be accommodated and no manual efforts will be required during reloading. With this approach, however, the ram pistons will be extended some distance outward from the aircraft body after stores ejection, increasing aerodynamic drag on the aircraft accordingly.
Conventional stores ejection mechanisms, therefore, suffer from the limitations discussed above. In particular, some conventional stores ejection mechanisms require manual action to adjust ejection rams into contact with stores after stores loading. Other conventional mechanisms protrude from the aircraft after stores ejection, increasing aircraft aerodynamic drag.